The present application pertains to the field of NFC technology. NFC is a short-range, standards-based wireless connectivity technology which is based on radio frequency identification, RFID, technology that uses magnetic field induction to enable communication between electronic devices in close proximity. NFC operates in the standard unlicensed 13.56 MHz frequency band over a distance of up to approximately 20 cm. Two modes of operation are defined by NFC protocols: active and passive. In active mode a device, which can either take up the role of a reader-writer or of an NFC tag, generates its own field to transmit data. The generation of its own field is also called active load modulation (ALM). Devices employing ALM are called active devices. On the other hand, in passive mode a device uses load modulation to transfer data in accordance with what is well-known to a person skilled in the art.
When implementing NFC technology in, for example, smartphones and smart watches, ALM has replaced the passive load modulation, because it allows the antenna size to be significantly reduced.
In order for two NFC devices to communicate, the devices have to detect or discover each other. Device detection is a process that runs on an NFC device with the purpose of enabling communication with a communication partner, i.e., another NFC device.
Existing mechanisms for device detection are low power card detection on the one side, and on the other side low power field detection. Thereby low power card detection allows an active NFC device, for instance a phone, to detect a passive tag. Low power field detection enables card emulation devices, for example phones or smart watches, to detect a magnetic field generated by an NFC reader device. The low power card detection relies on the loading effect between two devices which is based on magnetic induction. A first active device therefore periodically sends out pulses and monitors one or several electrical parameters, for example amplitude and/or phase, of these pulses. A second NFC device, which is not necessarily an active device, loads the first device when located in close proximity. The loading effect has an impact on the electrical characteristics of the pulses sent out by the first device. By noticing changes in the monitored electrical parameters the first device detects the presence of the second device. Once the second device is detected, the first device can initiate an NFC forum compliant reader/writer operation or a peer-to-peer transaction as defined in the NFC forum standards.
In the case that the second device is an active device which uses ALM, the second device may have a very small antenna which reduces the loading effect on the first device and consequently considerably diminishes the detection distance. The reduced detection distance renders the existing low power card detection scheme unsuitable for scenarios with two active devices.